The present invention relates to a fiber optic communication link, and more particularly to a short length, very high data rate, communication link.
One problem in transmitting information through standard electrical cables is the undesirable effect of radiated and conducted EMI (electro-magnetic interference) normally associated with these cables. Such EMI may, for example, cause spurious or other erroneous readings from equipment attached to the cable. One solution to this problem has been to convert the information to be transmitted from electrical energy to light energy, transmit the light energy signal through a light conducting cable such as, for example, a fiber optic bundle, and reconvert the light energy into electrical energy at the receiving end. Since the light conducting cable is not responsive to EMI, interference on the line is thus eliminated.
Fiber optic technology is being considered for future applications in two distinct areas of the data communication field. The first of these application areas, which is presently under intensive development, is concerned with the transmission of data over medium to long distances. Long distance data transmission utilizes low loss optical fiber, avalanche photodiode detectors with special low noise preamplifiers and bias stabilization circuits, thermoelectrically cooled laser diodes, and periodic repeater stages. Because of the potentially large commercial application for long distance optical data transmission, much privately sponsored research is directed towards this area. Medium and long distance optical communication links are also of considerable interest to the military departments.
The second area of development is concerned with the optical transmission of data over short distances of a few hundred meters or less. The advantages to be gained over the use of conventional wire cables include: higher per channel data rate capability, immunity to electromagnetic interference, lower cable weight, elimination of fire hazard due to electrical shorting, and potentially lower cost. For short length data link applications, multi-fiber bundles of medium and high loss fiber are utilized. Light emitting diodes (LED's) are employed as optical sources, and photodiodes are used for optical detection. Short distance optical data transmission is of particular interest to the military departments since this technology has been proposed for the optical wiring of aircraft where line lengths of 150 feet or less are encountered.
Heretofore available existing equipment lack DC coupling and do not provide high data rate capability for high performance applications. Also the circuits are excessively complex, require numerous, non-standard power supply voltages and are suitable only for room temperature, non-military applications.